In beverages and fruits the lingering tactile sensation of astringency, as well as the persistent taste of bitterness, are primarily elicited by flavonoid phenols. Chemically, relative astringency of a compound is defined by its effectiveness in precipitating protein. As the degree of polymerization of tannin increases, bitterness decreases, while astringency increases. The astringent flavanol polymers or condensed tannins have a strong affinity for binding with proline rich proteins, such as those found in saliva. Sensorially astringency is a drying or rough mouthfeel thought to result from decreased oral lubrication, following binding of salivary proteins by tannins. This may explain the increase in intensity of astringency over several sips or wine or tea. Also consistent with this hypothesis, subjects with low salivary flow rates perceive astringency more intensely than high-flow individuals.
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